The semiconductor integrated circuit (IC) industry has experienced rapid growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while feature size (i.e., the smallest component that can be created using a fabrication process) has decreased. This scaling-down process generally provides benefits by increasing production efficiency and lowering associated costs.
One method used by the industry to meet the demand for device density is the adoption of damascene and dual-damascene structures for interconnect structures. In a damascene process, an underlying insulating layer is patterned with open trenches. Afterwards, a conductor is deposited and polished to the level of the insulating layer to form a patterned conductor feature. Dual-damascene processes use a similar approach in that two features (a trench and a via hole) are formed and filled with a single deposition of conductor.
However, as feature sizes shrink further and density requirements increase, the pitch between features, such as interconnect structures, decreases. As a result, fabrication processes continue to become more difficult to perform. It is a challenge to form interconnect structures with shorter and shorter pitches in a semiconductor device.